TypeError f is undefined when returning a record update from the server to the client

jomo.c

Trying to hook up a client/server interface for record updates. Alles gute until the very last mile: after returning the response to the client I get this error:

                             TypeError: f is undefined
                             dataTables.editor.js (line 252 col 138)

The response is:

  {"data":[{"planid":null,"evnamelast":"Duck","eveligibleincome":3232,"DT_RowId":10003869,"evnamefirst"

:"Daffy","estart":1440054000000,"eligibilityversionid":10003869,"evpositionname":"Duck duck goose"}]
}

The columns are setup as follows:

       var dispCols = [{
                   data: null,
                   defaultContent: '',
                   className: 'select-checkbox',
                   orderable: false
               },
               { data: "evnamefirst" },
               { data: "evnamelast" },
               { data: "evpositionname" },
               { data: "planid" },
               { data: "estart" },
               { data: "eveligibleincome", render: $.fn.dataTable.render.number( ',', '.', 0, '$' ) }
           ];

And the DataTables setup as:

        //Define the Editor
editor = new $.fn.dataTable.Editor( {
        ajax: {
            "url": "/grid?pAction=UpdateRecs&recType=" + recType,
            "dataSrc": ""
        },  
        idSrc: "eligibilityversionid",
        table: "#" + GRID_ID,
        /*fields: columns */
        fields: fields

    } );

//Setup DataTable
var table = $GRID.DataTable( {
    dom: "Bfrtip",
    ajax: {
        "url": "/grid?pAction=GetRecords&recType=" + recType,
        "dataSrc": ""
    },        
    columns: dispCols,
    select: {
        style:    'os',
        selector: 'td:first-child'

    },
    buttons: [
        { extend: "create", editor: editor },
        { extend: "edit",   editor: editor },
        { extend: "remove", editor: editor }
    ]
} );

DataTables debugger reference: awexub

web-page link: https://ibttest.claresco.com/grid?recType=Elig

Thanks in advance!